Cerebral aneurysms are sac-like expansions of arteries in the brain. If left untreated, some may rupture causing death or impairment. Endovascular coiling is a recent and increasingly popular method of treatment. Here the aneurysm sac is accessed by a catheter and filled with coils, which should induce formation of a clot inside the aneurysm. The coil-clot mass will disallow entry of blood and hence protect the aneurysm from rupture and bleeding. But in some patients, within months to years of the procedure, blood is noted to re-enter the sac, a complication called recurrence. Recurrence can occur in 10-30% of patients treated with coils. The causes of recurrence are poorly understood. It is important to understand what causes recurrence because that is the first step in addressing this challenge and reducing its incidence. It will also significantly impact intervention strategie for aneurysm patients. The overall goal of this project is to shed light on the mechanisms underlying recurrence. Conventional thinking holds that recurrence occurs because the coil mass compacts itself (i.e., reduces in size) inside the sac over time, making room for blood to re-enter it. Plausible as this may seem, preliminary studies performed by employing rigorous three-dimensional image analysis techniques with a pilot population suggest otherwise. The primary hypothesis of this study is that the mechanism for recurrence is the growth of the aneurysm sac itself, not necessarily coil compaction Specific aim #1 of the project is to test the hypothesis in a statistically powered population of 25 coil-embolized aneurysm patients presenting with recurrence. Three dimensional image processing and computational analysis tools will be leveraged for accurate reconstructions and estimations of the aneurysm sac and coil mass volumes from rotational angiography scans in order to assess whether sac growth exists in recurrence subjects. Further, it would be quite beneficial to identify if some measurable metrics of aneurysm morphology or treatment procedure ay serve as risk factors for recurrence. The applicants' group has developed computational morphometric tools for rigorously quantifying the three-dimensional morphology of patient- specific aneurysms into size and shape metrics. Specific aim #2 is to compare metrics of morphology and procedure between the recurrence-prone population from aim #1 with a control population (i.e., coiled aneurysms that do not show recurrence) that is size and location-matched. The goal is to ascertain which, if any, of the patient-specific measurable metrics may serve as prognostic indicators of recurrence. Identifying risk factors of recurrence may help identify and avoid patients prone to this major complication from this otherwise safe and effective procedure. If the results in aim #1 are consistent with proposed hypothesis that recurrence is associated with sac growth, patients with growing aneurysms are not suitable candidates for this procedure. The proposed project therefore can significantly impact clinical management of aneurysm patients.